Navy developing an integrally sound- and thermally-suppressed M4

The Naval Special Warfare Center – Crane is developing an M4 that has integral suppression for both sound and thermal signature! They're calling it Suppressed Upper Receiver Group (SURG). I just heard about this today, it's very cool, and the engineering geek in me is excited and wants to share.

Apparently, bad guys are learning to locate our soldiers via the thermal signature of their rifles, using either looted or black market thermal imagers, or modified civilian still/video cameras with the CCD/CMOS sensor's IR filter removed.

The problem is complex:
All the heat generated has to go somewhere – you can't make it just magically disappear (conservation of energy and all).
Protect the user and attached accessories from 500° - 1,000° heat that's less than an inch away, inside the fore end.
Incorporate a sound suppressor.
Create no muzzle flash.
Produce 2,600fps velocity, 3" groups at 100 yards, and last 15,000 rounds. This is both a design and materials problem, as the SURG will be subject to much higher thermal stresses than a standard M4 upper.

My understanding of the solution is that it's simple in concept, but challenging in practice:
Heat from the barrel, silencer and muzzle device is contained within an insulated sleeve. It sounds like they're going with Insulon, which is the same idea as the old vacuum-insulated Thermos, but made of metal sheets instead of glass. The vacuum space can be very small – in this case only about 1 millimeter across – and still be extremely effective. This vacuum space halts conductive and convective cooling, meaning little to no heat signature, and both the user and fore end-mounted accessories are protected.
So where does that heat go? This the neat part: with any gun, some of the muzzle blast travels backwards towards the user (this is what you wear ear pro for – duh). The SURG design uses this blast like a fan to push cool air into the muzzle end of the Insulon sleeve, along the barrel and over the barrel nut (which doubles as a finned heat sink), and then diffuses the now-hot air into the surrounding air, cooling it enough to reduce the thermal signature. If it helps, this is the same idea behind engine outlets of the B2 bomber or A-10 Warthog, where the outlets are recessed (B2) or hidden (A-10) behind part of the airframe, which blocks direct view from below of the hot outlet gasses, and allowing the exhaust to mix with surrounding air and cool a bit before it's visible to a heat-seeking SAM below.
The sound suppressor is also crazy innovative: It's a reflex design, meaning it extends back along the barrel, nested between the barrel and the Insulon sleeve. The barrel is ported in several places along its length, diverting a pre-determined amount of gas into the suppressor, like the old MP5N did. Towards the end of the barrel is a baffle stack, sort of like a standard suppressor, except for two oddities mentioned in the patent: the use of elastic materials in the baffles – the hot gas would transfer its energy and heat by stretching this material; and the use of movable baffles – similarly, moving the baffles would transfer energy away from the gas.
Finally, the SURG will accept any standard flash hider or brake. Presumably, you could attach another suppressor, because, like Xzibit says, I heard you like suppressors, so I put a suppressor on your suppressor so you can suppress while you're suppressing (Hmm, maybe the wrong crowd for that reference).
I have no formal training as an engineer or physicist, but I do understand a bit of the engineering and physics concepts underpinning how this works. So, I'll try to answer any questions that I can, and I'll say "I don't know" when I don't.

In case there's concern about op-sec / info-sec, all of this is publicly available in the patent and two non-classified presentations, linked below.

interesting concept. I wonder if they thought about or tested using an inert gas injection system to help cool the can, say nitrogen or CO2. This would not only cool the internals of the suppressor but using inert gas also helps by acting like a fire extinguisher when the gasses from the fired round enter the can making it more efficient as it puts out any remaining burning particles/gasses. The obvious down side would be having to carry inert gas cartridges adding weight as well as being dependent upon another supply.

I would think NASA rocket motor coatings would be a really good use here! This coating can withstand unbelievable heat! I have seen it used for Steam Generators in Steam Boiler's! It's pretty incredible what these can do! I can see going back to a wipe system internally with the silencers to keep the noise and gasses enclosed and venting slowly out of the system! I would think the sound energy would still be the #1 issue here! I would also think training with this type of system would mitigate much of the other issues! I am thinking these would be used by

If they are using thermal imaging devices...won't they still pick up the human heat signature?

Click to expand...

They might be able to, though it depends on the distance between them, the difference in temperature between the person and the background (a hot barrel might be 500° hotter than the background, while a person might only be a 10° or 20° hotter on a warm summer night), and mostly on the thermal imaging device being used.

A current-gen, high-resolution imager, like our soldiers use, can detect a larger swath of the IR spectrum (IR isn't just one frequency, it's a huge range), and it can pick up a heat signature that's smaller in size, fainter relative to the background, and further away than an older or lower-resolution imager.

If the bad guy is using a camcorder with its IR filter removed, he's going to see the landscape mostly in the visible spectrum, just like a camcorder with its IR filter intact, only there might be a light-gray fleck here or there, indicating a heat source. The sensor in a camcorder isn't all that sensitive to IR, and mostly to the near-band frequencies. And those flecks will be pretty hard to distinguish from the clutter of rocks, shrubs, dirt, trees, etc. without the superimposed color from a purpose-built imager.

Step 1. Dream up a scenario
Step 2. Get a $1 Million grant to study a non existent problem.
Step 3. Engineer an over the top solution to a non existent problem.
Step 4. Spend $4 Billion developing a solution to a non existent problem.
Step 5. Kill the program after spending $4 Billion on non existent problem and put nothing in the field.
Step 6. Wrap barrel and silencer with wet towel.

I know a very successful local Portland artist that once told me it's not the ability to make award winning art per say, it's the ability to write top notch grant submissions that awards you the money to produce mediocre art.

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